Multi charged particle beam writing apparatus and multi charged particle beam writing method

ABSTRACT

A multiple charged particle beam writing apparatus includes a circuitry to calculate, for each of the plurality of combinations, a first distribution coefficient for each of the three beams configuring the combination concerned, for distributing a dose to irradiate the design grid concerned to the three beams such that the gravity center position of each distributed dose coincides with the position of the design grid concerned and the sum of the each distributed dose coincides with the dose to irradiate the design grid concerned; and a circuitry to calculate, for each of the four or more beams, a second distribution coefficient of each of the four or more beams relating to the design grid concerned by dividing the total value of at least one first distribution coefficient corresponding to the beam concerned in the four or more beams by the number of the plurality of combinations.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2017-149854 filed on Aug. 2, 2017in Japan, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relate to a multi charged particlebeam writing apparatus and a multi charged particle beam writing method,and, for example, relate to a method for controlling the maximumirradiation time of multi-beam writing.

Description of Related Art

The lithography technique that advances miniaturization of semiconductordevices is extremely important as a unique process whereby patterns areformed in semiconductor manufacturing. In recent years, with highintegration of LSI, the line width (critical dimension) required forsemiconductor device circuits becomes progressively narrower year byyear. The electron beam writing technique, which intrinsically hasexcellent resolution, is used for writing or “drawing” a mask pattern ona mask blank with electron beams.

For example, as a known example of employing the electron beam writingtechnique, there is a writing apparatus using multiple beams. Since itis possible for multi-beam writing to irradiate multiple beams at atime, the writing throughput can be greatly increased in comparison withsingle electron beam writing. For example, a writing apparatus employingthe multi-beam system forms multiple beams by letting portions of anelectron beam emitted from an electron gun individually pass through acorresponding one of a plurality of holes in a mask, performs blankingcontrol for each beam, reduces each unblocked beam by an optical systemin order to reduce a mask image, and deflects the beam by a deflector toirradiate a desired position on a target object or “sample”.

In multi-beam writing, the dose of each beam is controlled based on theirradiation time. However, since irradiation of multiple beams iscarried out at the same time, the shot time per shot is rate-controlledbased on the maximum irradiation time of each beam. Thus, when movingthe stage continuously at a constant speed, the stage speed is definedby the speed which enables to perform irradiation of the maximumirradiation time in all the shots of multiple beams. Accordingly, theshot of the maximum irradiation time restricts the shot cycle and thestage speed. If the maximum irradiation time increases, the throughputof the writing apparatus decreases correspondingly to the increasedtime.

For the dose of each beam, dose modulation is performed in order tocorrect dimension variations occurred due to a phenomenon such as aproximity effect. In multiple beams, distortion occurs in an exposurefield due to optical system characteristics, and therefore, theirradiation position of each beam deviates from the ideal grid becauseof the distortion. However, in multiple beams, it is difficult todeflect each beam individually, thereby being difficult to individuallycontrol the position of each beam on the target object surface.Accordingly, there is disclosed that positional deviation of each beamis corrected by dose modulation (e.g., refer to Japanese PatentApplication Laid-open No. 2016-103557). The level of a dose to irradiateeach irradiation position in the case of performing dose modulationneeds to be, for example, several hundred percent of that of the basedose. Therefore, the maximum irradiation time becomes further increased.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a multiple chargedparticle beam writing apparatus includes

-   -   an emission source configured to emit a charged particle beam;    -   a shaping aperture array substrate configured to form multiple        charged particle beams by being irradiated with the charged        particle beam;    -   a combination setting circuitry configured to set, for each of a        plurality of design grids being irradiation positions in design        of the multiple charged particle beams, a plurality of        combinations each composed of three beams whose actual        irradiation positions surround a design grid concerned in the        plurality of design grids, by using four or more beams whose        actual irradiation positions are close to the design grid        concerned;    -   a first distribution coefficient calculation circuitry        configured to calculate, for each of the plurality of        combinations, a first distribution coefficient for each of the        three beams configuring a combination concerned in the plurality        of combinations, for distributing a dose to irradiate the design        grid concerned to the three beams configuring the combination        concerned such that a position of a gravity center of each        distributed dose coincides with a position of the design grid        concerned and a sum of the each distributed dose coincides with        the dose to irradiate the design grid concerned, where at least        one the first distribution coefficient is calculated for the        each of the four or more beams;    -   a second distribution coefficient calculation circuitry        configured to calculate, for each of the four or more beams, a        second distribution coefficient of the each of the four or more        beams relating to the design grid concerned by dividing a total        value of the at least one the first distribution coefficient        corresponding to a beam concerned in the four or more beams by a        number of the plurality of combinations; and    -   a writing mechanism configured to write a pattern on a target        object with the multiple charged particle beams in which the        dose to irradiate each of the plurality of design grids has been        distributed to each corresponding one of the four or more beams.

According to another aspect of the present invention, a multiple chargedparticle beam writing method includes

-   -   setting, for each of a plurality of design grids being        irradiation positions in design of multiple charged particle        beams, a plurality of combinations each composed of three beams        whose actual irradiation positions surround a design grid        concerned in the plurality of design grids, by using four or        more beams whose actual irradiation positions are close to the        design grid concerned;    -   calculating, for each of the plurality of combinations, a first        distribution coefficient for each of the three beams configuring        a combination concerned in the plurality of combinations, for        distributing a dose to irradiate the design grid concerned to        the three beams configuring the combination concerned such that        a position of a gravity center of each distributed dose        coincides with a position of the design grid concerned and a sum        of the each distributed dose coincides with the dose to        irradiate the design grid concerned, where at least one the        first distribution coefficient is calculated for the each of the        four or more beams;    -   calculating, for each of the four or more beams, a second        distribution coefficient of the each of the four or more beams        relating to the design grid concerned by dividing a total value        of the at least one the first distribution coefficient        corresponding to a beam concerned in the four or more beams by a        number of the plurality of combinations; and    -   writing a pattern on a target object with the multiple charged        particle beams in which the dose to irradiate each of the        plurality of design grids has been distributed to each        corresponding one of the four or more beams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a configuration of a writingapparatus according to a first embodiment;

FIG. 2 is a conceptual diagram showing a configuration of a shapingaperture array substrate according to the first embodiment;

FIG. 3 is a sectional view showing a configuration of a blankingaperture array mechanism according to the first embodiment;

FIG. 4 is a top view conceptual diagram showing a portion of thestructure in a membrane region of a blanking aperture array mechanismaccording to the first embodiment;

FIG. 5 shows an example of an individual blanking mechanism according tothe first embodiment;

FIG. 6 is a conceptual diagram explaining an example of a writingoperation according to the first embodiment;

FIG. 7 shows an example of an irradiation region of multiple beams and apixel to be written according to the first embodiment;

FIG. 8 illustrates an example of a writing method of multiple beamsaccording to the first embodiment;

FIG. 9 is a flowchart showing main steps of a writing method accordingto the first embodiment;

FIGS. 10A and 10B illustrate a beam positional deviation and apositional deviation periodicity according to the first embodiment;

FIG. 11 is a flowchart showing an example of internal steps of the dosedistribution table generation step according to the first embodiment;

FIG. 12 illustrates a method of searching for a proximity beam accordingto the first embodiment;

FIG. 13 shows an example of a control grid and an actual irradiationposition of each beam according to the first embodiment;

FIGS. 14A to 14D illustrate a method for distributing a dose tosurrounding three proximity beams according to the first embodiment;

FIG. 15 shows an example of a dose distribution table according to thefirst embodiment;

FIGS. 16A and 16B show examples of a dose frequency based on dosedistribution according to the first embodiment;

FIG. 17 is a conceptual diagram showing a configuration of a writingapparatus according to a second embodiment;

FIG. 18 is a flowchart showing main steps of a writing method accordingto the second embodiment;

FIG. 19 is a flowchart showing steps in the dose distribution tableadjustment step according to the second embodiment;

FIG. 20 shows an example of a dose map in the case of assuming the areadensity of uniformly 100% according to the second embodiment;

FIG. 21 illustrates a method of searching for a proximity beam close toa specific beam whose distributed dose amount exceeds a thresholdaccording to the second embodiment;

FIG. 22 shows an example of a dose distribution table after correctionaccording to the second embodiment;

FIG. 23 is a conceptual diagram showing a configuration of a writingapparatus according to a third embodiment;

FIG. 24 is a flowchart showing main steps of a writing method accordingto the third embodiment; and

FIGS. 25A and 25B show examples of dispersion at the edge due to dosedistribution and a dose frequency according to the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments below describe an apparatus and method which can shorten themaximum irradiation time in multi-beam writing.

Embodiments below describe a configuration in which an electron beam isused as an example of a charged particle beam. The charged particle beamis not limited to the electron beam, and other charged particle beamsuch as an ion beam may also be used.

First Embodiment

FIG. 1 is a schematic diagram showing a configuration of a writing or“drawing” apparatus according to a first embodiment. As shown in FIG. 1,a writing apparatus 100 includes a writing mechanism 150 and a controlsystem circuit 160. The writing apparatus 100 is an example of a multicharged particle beam writing apparatus. The writing mechanism 150includes an electron optical column 102 (multi electron beam column) anda writing chamber 103. In the electron optical column 102, there arearranged an electron gun 201, an illumination lens 202, a shapingaperture array substrate 203, a blanking aperture array mechanism 204, areducing lens 205, a limiting aperture substrate 206, an objective lens207, a deflector 208, and a deflector 209. In the writing chamber 103,there is arranged an XY stage 105. On the XY stage 105, a target objector “sample” 101 such as a mask blank, on which resist is applied,serving as a writing target substrate is placed when writing isperformed. The target object 101 is, for example, an exposure mask usedfor fabricating semiconductor devices, or a semiconductor substrate(silicon wafer) for fabricating semiconductor devices. Moreover, amirror 210 for measuring the position of the XY stage 105 is arranged onthe XY stage 105.

The control system circuit 160 includes control computer 110, a memory112, a deflection control circuit 130, digital-to-analog converting(DAC) amplifier units 132 and 134, a stage position detector 139, andstorage devices 140, 142, and 144, such as magnetic disk drives. Thecontrol computer 110, the memory 112, the deflection control circuit130, the DAC amplifier units 132 and 134, the stage position detector139, and the storage devices 140, 142, and 144 are connected with eachother through a bus (not shown). The deflection control circuit 130 isconnected to the DAC amplifier units 132 and 134, and a blankingaperture array mechanism 204. Outputs of the DAC amplifier unit 132 areconnected to the deflector 209. Outputs of the DAC amplifier unit 134are connected to the deflector 208. The stage position detector 139irradiates the mirror 210 on the XY stage 105 with a laser beam, andreceives a reflected light from the mirror 210. Then, the stage positiondetector 139 measures the position of the XY stage 105 by using theprinciple of the laser interference based on information on thereflected light.

In the control computer 110, there are arranged a rasterizing unit 50, adose map generation unit 52, a beam-positional-deviation map generationunit 54, a selection unit 56, a search unit 58, a combination settingunit 60, a dose distribution ratio calculation unit 62, a dosedistribution coefficient calculation unit 64, a dose distribution tablegeneration unit 66, a dose modulation unit 68, and a writing controlunit 72. Each of “ . . . units” such as the rasterizing unit 50, thedose map generation unit 52, the beam-positional-deviation mapgeneration unit 54, the selection unit 56, the search unit 58, thecombination setting unit 60, the dose distribution ratio calculationunit 62, the dose distribution coefficient calculation unit 64, the dosedistribution table generation unit 66, the dose modulation unit 68, andthe writing control unit 72 includes a processing circuitry. As theprocessing circuitry, for example, an electric circuit, computer,processor, circuit board, quantum circuit, or semiconductor device isused. Each “ . . . unit” may use a common processing circuitry (sameprocessing circuitry), or different processing circuitries (separateprocessing circuitries). Information input and output to/from therasterizing unit 50, the dose map generation unit 52, thebeam-positional-deviation map generation unit 54, the selection unit 56,the search unit 58, the combination setting unit 60, the dosedistribution ratio calculation unit 62, the dose distributioncoefficient calculation unit 64, the dose distribution table generationunit 66, the dose modulation unit 68, and the writing control unit 72,and information being operated are stored in the memory 112 each time.

Moreover, writing data is input from the outside of the writingapparatus 100, and stored in the storage device 140. The writing datausually defines information on a plurality of figure patterns to bewritten. Specifically, it defines a figure code, coordinates, size, etc.of each figure pattern.

FIG. 1 shows structure elements necessary for describing the firstembodiment. It should be understood that other structure elementsgenerally necessary for the writing apparatus 100 may also be includedtherein.

FIG. 2 is a conceptual diagram showing a configuration of a shapingaperture array substrate according to the first embodiment. As shown inFIG. 2, holes (openings, apertures) 22 of p rows long (length in the ydirection) and q columns wide (width in x direction) (p≥2, q≥2) areformed, like a matrix, at a predetermined arrangement pitch in theshaping aperture array substrate 203. In FIG. 2, for example, holes 22of 512 (rows of holes arrayed in y direction)×512 (columns of holesarrayed in x direction) are formed. Each of the holes 22 is a quadrangle(rectangle) having the same dimension and shape. Alternatively, each ofthe holes 22 may be a circle with the same diameter. By making portionsof an electron beam 200 individually pass through a corresponding holeof a plurality of holes 22, multiple beams 20 are formed. The method ofarranging the holes 22 is not limited to the case of FIG. 2 where holesare arranged in a grid form in the length and width directions. Forexample, with respect to the kth and the (k+1)th rows which are arrayed(accumulated) in the length direction (y direction), each hole in thekth row and each hole in the (k+1)th row may be mutually displaced inthe width direction (x direction) by a dimension “a”. Similarly, withrespect to the (k+1)th and the (k+2)th rows which are arrayed(accumulated) in the length direction (y direction), each hole in the(k+1)th row and each hole in the (k+2)th row may be mutually displacedin the width direction (x direction) by a dimension “b”, for example.

FIG. 3 is a sectional view showing a configuration of a blankingaperture array mechanism according to the first embodiment.

FIG. 4 is a top view conceptual diagram showing a portion of thestructure in a membrane region of a blanking aperture array mechanismaccording to the first embodiment. The position relation of a controlelectrode 24, a counter electrode 26, a control circuit 41, and a pad 43in FIG. 3 is not in accordance with that of FIG. 4. With regard to thestructure of the blanking aperture array mechanism 204, a semiconductorsubstrate 31 made of silicon, etc. is placed on a support table 33. Thecentral part of the substrate 31 is shaved from the back side, and madeinto a membrane region 330 (first region) having a thin film thicknessh. The periphery surrounding the membrane region 330 is an outerperipheral region 332 (second region) having a thick film thickness H.The upper surface of the membrane region 330 and the upper surface ofthe outer peripheral region 332 are formed to be flush or substantiallyflush in height with each other. At the back side of the outerperipheral region 332, the substrate 31 is supported on the supporttable 33. The central part of the support table 33 is open, and themembrane region 330 is located at this opening region.

In the membrane region 330, passage holes 25 (openings) through each ofwhich a corresponding one of multiple beams passes are formed atpositions each corresponding to each hole 22 of the shaping aperturearray substrate 203 shown in FIG. 2. In other words, in the membraneregion 330 of the substrate 31, there are formed a plurality of passageholes 25 in an array through each of which a corresponding beam ofelectron multiple beams passes. Moreover, in the membrane region 330 ofthe substrate 31, there are arranged a plurality of electrode pairs eachcomposed of two electrodes being opposite to each other with respect toa corresponding one of a plurality of passage holes 25. Specifically, inthe membrane region 330, as shown in FIGS. 3 and 4, each pair (blanker:blanking deflector) of the control electrode 24 and the counterelectrode 26 for blanking deflection is arranged close to acorresponding passage hole 25 in a manner such that the electrodes 24and 26 are opposite to each other across the passage hole 25 concerned.Moreover, close to each passage hole 25 in the membrane region 330 ofthe substrate 31, there is arranged the control circuit 41 (logiccircuit) for applying a deflection voltage to the control electrode 24for the passage hole 25 concerned. The counter electrode 26 for eachbeam is grounded (earthed).

As shown in FIG. 4, n-bit (e.g., 10-bit) parallel lines for controlsignals are connected to each control circuit 41. In addition to then-bit parallel lines for controlling signals, lines for a clock signal,a read signal, a shot signal, a power supply, and the like are connectedto each control circuit 41. Alternatively, a part of the parallel linesmaybe used as the lines for a clock signal, a read signal, a shotsignal, a power supply, and the like. An individual blanking mechanism47 composed of the control electrode 24, the counter electrode 26, andthe control circuit 41 is configured for each of the multiple beams. Inthe example of FIG. 3, the control electrode 24, the counter electrode26, and the control circuit 41 are arranged in the membrane region 330having a thin film thickness of the substrate 31. However, it is notlimited thereto. A plurality of control circuits 41 formed in an arrayin the membrane region 330 are grouped, for example, per row or percolumn, and the control circuits 41 in each group are connected inseries as shown in FIG. 4. Then, the pad 43 arranged for each groupsends a signal to the control circuits 41 in the group concerned.Specifically, a shift register (not shown) is arranged in each controlcircuit 41, and for example, shift registers in the control circuits 41for beams in the same row in p×g multiple beams, for example, areconnected in series. For example, control signals for beams in the samerow in the p×q multiple beams are transmitted in series, and, forexample, a control signal for each beam is stored in a correspondingcontrol circuit 41 by p clock signals totally.

FIG. 5 shows an example of an individual blanking mechanism according tothe first embodiment. As shown in FIG. 5, an amplifier 46 (an example ofa switching circuit) is arranged in the control circuit 41. In the caseof FIG. 5, a CMOS (complementary MOS) inverter circuit is arranged as anexample of the amplifier 46. The CMOS inverter circuit is connected to apositive potential (Vdd: blanking electric potential: first electricpotential) (e.g., 5 V) (first electric potential) and to a groundpotential (GND: second electric potential). The output line (OUT) of theCMOS inverter circuit is connected to the control electrode 24. On theother hand, the counter electrode 26 is applied with a ground electricpotential. A plurality of control electrodes 24, each of which isapplied with a blanking electric potential and a ground electricpotential in a switchable manner, are arranged on the substrate 31 suchthat each control electrode 24 and the corresponding counter electrode26 are opposite to each other with respect to a corresponding one of aplurality of passage holes 25.

As an input (IN) of each CMOS inverter circuit, either an L (low)electric potential (e.g., ground potential) lower than a thresholdvoltage, or an H (high) electric potential (e.g., 1.5 V) higher than orequal to the threshold voltage is applied as a control signal. Accordingto the first embodiment, in a state where an L electric potential isapplied to the input (IN) of the CMOS inverter circuit, the output (OUT)of the CMOS inverter circuit becomes a positive potential (Vdd), andthen, a corresponding beam 20 is deflected by an electric field due to apotential difference from the ground potential of the counter electrode26 so as to be blocked by the limiting aperture substrate 206, therebybeing controlled to be in a beam OFF condition. On the other hand, in astate (active state) where an H electric potential is applied to theinput (IN) of the CMOS inverter circuit, the output (OUT) of the CMOSinverter circuit becomes a ground potential, and therefore, since thereis no potential difference from the ground potential of the counterelectrode 26, a corresponding beam 20 is not deflected, thereby beingcontrolled to be in a beam ON condition by making the beam concernedpass through the limiting aperture substrate 206.

The electron beam 20 passing through a corresponding passage hole isdeflected by a voltage independently applied to a pair of the controlelectrode 24 and the counter electrode 26. Blanking control is performedby this deflection. Specifically, a pair of the control electrode 24 andthe counter electrode 26 individually provides blanking deflection of acorresponding beam of multiple beams by an electric potential switchableby the CMOS inverter circuit which serves as a corresponding switchingcircuit. Thus, each of a plurality of blankers performs blankingdeflection of a corresponding beam in the multiple beams having passedthrough a plurality of holes 22 (openings) in the shaping aperture arraysubstrate 203.

FIG. 6 is a conceptual diagram explaining an example of a writingoperation according to the first embodiment. As shown in FIG. 6, awriting region 30 of the target object 101 is virtually divided by apredetermined width in the y direction into a plurality of striperegions 32 in a strip form, for example. First, the XY stage 105 ismoved to make an adjustment such that an irradiation region 34 which canbe irradiated with one shot of the multiple beams 20 is located at theleft end of the first stripe region 32 or at a position further leftthan the left end, and then writing is started. When writing the firststripe region 32, the XY stage 105 is moved, for example, in the −xdirection, so that the writing proceeds relatively in the x direction.The XY stage 105 is moved, for example, continuously at a constantspeed. After writing the first stripe region 32, the stage position ismoved in the −y direction to make an adjustment such that theirradiation region 34 is located at the right end of the second striperegion 32 or at a position further right than the right end and locatedrelatively in the y direction. Then, by moving the XY stage 105 in the xdirection, for example, writing proceeds in the −x direction. That is,writing is performed while alternately changing the direction, such asperforming writing in the x direction in the third stripe region 32, andin the −x direction in the fourth stripe region 32, thereby reducing thewriting time. However, the writing operation is not limited to thewriting while alternately changing the direction, and it is alsopreferable to perform writing in the same direction when writing eachstripe region 32. A plurality of shot patterns up to as many as thenumber of the holes 22 are formed at a time by one shot of multiplebeams having been formed by passing through the holes 22 in the shapingaperture array substrate 203.

FIG. 7 shows an example of an irradiation region of multiple beams and apixel to be written (writing target pixel) according to the firstembodiment. In FIG. 7, in the stripe region 32, there are set aplurality of control grids 27 (design grids) arranged in a grid form atthe beam size pitch of the multiple beams 20 on the surface of thetarget object 101, for example. Preferably, they are arranged at anarrangement pitch of around 10 nm. A plurality of control grids 27 serveas design irradiation positions of the multiple beams 20. Thearrangement pitch of the control grid 27 is not limited to the beamsize, and may be an arbitrary size which can be controlled as adeflecting position of the deflector 209, regardless of the beam size.Then, a plurality of pixels 36 obtained by virtually dividing into amesh form by the same size as that of the arrangement pitch of thecontrol grid 27 are set, each of which is centering on each control grid27. Each pixel 36 serves as an irradiation unit region per beam ofmultiple beams. FIG. 7 shows the case where the writing region of thetarget object 101 is divided, for example, in the y direction, into aplurality of stripe regions 32 by the width size being substantially thesame as the size of the irradiation region 34 (writing field) which canbe irradiated with one irradiation of the multiple beams 20. The size inthe x direction of the irradiation region 34 can be defined by the valueobtained by multiplying the pitch between beams in the x direction ofthe multiple beams 20 by the number of beams in the x direction. Thesize in the y direction of the irradiation region 34 can be defined bythe value obtained by multiplying the pitch between beams in the ydirection of the multiple beams 20 by the number of beams in the ydirection. The width of the stripe region 32 is not limited to this.Preferably, the width of the stripe region 32 is n times (n being aninteger of 1 or more) the size of the irradiation region 34. FIG. 7shows the case of multiple beams of 512×512 (rows×columns) beingsimplified to 8×8 (rows×columns). In the irradiation region 34, thereare shown a plurality of pixels 28 (beam writing positions) which can beirradiated with one shot of the multiple beams 20. In other words, thepitch between adjacent pixels 28 is the pitch between beams of thedesign multiple beams. In the example of FIG. 7, one sub-irradiationregion 29 is a square region surrounded by four adjacent pixels 28 atfour corners and including one of the four pixels 28. In the case ofFIG. 7, each sub-irradiation region 29 is composed of 4×4 pixels.

FIG. 8 illustrates an example of a writing method of multiple beamsaccording to the first embodiment. FIG. 8 shows a part of thesub-irradiation region 29 to be written by respective beams at thecoordinates (1, 3), (2, 3), (3, 3), . . . , (512, 3) in the third rowfrom the bottom in the multiple beams for writing the stripe region 32shown in FIG. 7. In the example of FIG. 8, while the XY stage 105 movesthe distance of eight beam pitches, four pixels are written (exposed),for example. In order that the relative position between the irradiationregion 34 and the target object 101 may not shift by the movement of theXY stage 105 while these four pixels are written (exposed), theirradiation region 34 is made to follow the movement of the XY stage 105by collectively deflecting the entire multiple beams 20 by the deflector208. In other words, tracking control is performed. In the example ofFIG. 8, one tracking cycle is executed by writing (exposing) four pixelswhile moving the distance of eight beam pitches.

Specifically, the stage position measuring instrument 139 measures theposition of the XY stage 105 by irradiating the mirror 210 with a laserand receiving a reflected light from the mirror 210. The measuredposition of the XY stage 105 is output to the control computer 110. Inthe control computer 110, the writing control unit 72 outputs theposition information on the XY stage 105 to the deflection controlcircuit 130. In accordance with the movement of the XY stage 105, thedeflection control circuit 130 calculates deflection amount data(tracking deflection data) for deflecting beams to follow the movementof the XY stage 105. The tracking deflection data being a digital signalis output to the DAC amplifier 134. The DAC amplifier 134 converts thedigital signal to an analog signal and amplifies it to be applied as atracking deflection voltage to the main deflector 208.

The writing mechanism 150 irradiates each control grid 27 with acorresponding beam in an ON state in the multiple beams 20 during awriting time (irradiation time or exposure time) corresponding to eachcontrol grid 27 within a maximum irradiation time Ttr of the irradiationtime of each of the multiple beams of the shot concerned.

In the example of FIG. 8, the control grid 27 of the first pixel 36 fromthe right in the bottom row of the sub-irradiation region 29 concernedis irradiated with the first shot of the beam (1) at coordinates (1, 3)during the time from t=0 to t=maximum irradiation time Ttr, for example.Thereby, the pixel concerned has received beam irradiation of a desiredirradiation time. The XY stage 105 moves two beam pitches in the −xdirection during the time from t=0 to t=Ttr, for example. During thistime period, the tracking operation is continuously performed.

After the maximum irradiation time Ttr of the shot concerned has passedsince the start of beam irradiation of the shot concerned, while thebeam deflection for tracking control is continuously performed by thedeflector 208, the writing position (previous writing position) of eachbeam is shifted to a next writing position (current writing position) ofeach beam by collectively deflecting the multiple beams 20 by thedeflector 209, which is performed in addition to the beam deflection fortracking control. In the example of FIG. 8, when the time becomes t=Ttr,the writing target control grid 27 to be written is shifted from thecontrol grid 27 of the first pixel 36 from the right in the bottom rowof the sub-irradiation region 29 concerned, to the control grid 27 ofthe first pixel 36 from the right in the second row from the bottom.Since the XY stage 105 is moving at a fixed speed also during this timeperiod, the tracking operation is continuously performed.

Then, while the tracking control is continuously performed, respectivecorresponding beams in the ON state in the multiple beams 20 are appliedto the shifted writing positions corresponding to the respective beamsduring a writing time corresponding to each of the respective beamswithin the maximum irradiation time Ttr of the shot concerned. In theexample of FIG. 8, the control grid 27 of the first pixel 36 from theright in the second row from the bottom of the sub-irradiation region 29concerned is irradiated with the second shot of the beam (1) at thecoordinates (1, 3) during the time from t=Ttr to t=2Ttr, for example.The XY stage 105 moves two beam pitches in the −x direction during thetime from t=Ttr to t=2Ttr, for example. During this time period, thetracking operation is continuously performed.

In the example of FIG. 8, when the time becomes t=2Ttr, the writingtarget control grid 27 to be written is shifted from the control grid 27of the first pixel 36 from the right in the second row from the bottomof the sub-irradiation region 29 concerned to the control grid 27 of thefirst pixel 36 from the right in the third row from the bottom. Sincethe XY stage 105 is moving also during this time period, the trackingoperation is continuously performed. Then, the control grid 27 of thefirst pixel 36 from the right in the third row from the bottom of thesub-irradiation region 29 concerned is irradiated with a beam of thethird shot of the beam (1) at the coordinates (1, 3) during the timefrom t=2Ttr to t=3Ttr, for example. Thereby, the control grid 27 of thepixel 36 concerned has received beam irradiation of a desiredirradiation time.

The XY stage 105 moves two beam pitches in the −x direction during thetime from t=2Ttr to t=3Ttr, for example. During this time period, thetracking operation is continuously performed. When the time becomest=3Ttr, the writing target grid 27 to be written is shifted from thecontrol grid 27 of the first pixel 36 from the right in the third rowfrom the bottom of the sub-irradiation region 29 concerned to thecontrol grid 27 of the first pixel 36 from the right in the fourth rowfrom the bottom by collectively deflecting the multiple beams by thedeflector 209. Since the XY stage 105 is moving also during this timeperiod, the tracking operation is continuously performed.

The control grid 27 of the first pixel 36 from the right in the fourthrow from the bottom of the sub-irradiation region 29 concerned isirradiated with a beam of the fourth shot of the beam (1) at thecoordinates (1, 3) during the time from t=3Ttr to t=4Ttr, for example.Thereby, the control grid 27 of the pixel 36 concerned has received beamirradiation of a desired irradiation time.

The XY stage 105 moves two beam pitches in the −x direction during thetime from t=3Ttr to t=4Ttr, for example.

During this time period, the tracking operation is continuouslyperformed. In this manner, writing of the pixels in the first columnfrom the right of the sub-irradiation region 29 concerned has beencompleted.

In the example of FIG. 8, after applying a corresponding beam to thewriting position of each beam which has been shifted three times fromthe initial position, the DAC amplifier unit 134 returns the trackingposition to the start position of tracking where the tracking controlwas started, by resetting the beam deflection for tracking control. Inother words, the tracking position is returned in the opposite directionto the direction of the stage movement. In the example of FIG. 8, whenthe time becomes t=4Ttr, tracking of the sub-irradiation region 29concerned is cancelled, and the beam is swung back to a newsub-irradiation region 29 which has been shifted by eight beam pitchesin the x direction. Although the beam (1) at the coordinates (1, 3) hasbeen described in the example of FIG. 8, writing is also similarlyperformed for each sub-irradiation region 29 corresponding to a beam atother coordinates. That is, the beam at coordinates (n, m) completeswriting of pixels in the first column from the right of a correspondingsub-irradiation region 29 when the time becomes t=4Ttr. For example, thebeam (2) at coordinates (2, 3) completes writing of pixels in the firstcolumn from the right of the sub-irradiation region 29 adjacent in the−x direction to the sub-irradiation region 29 for the beam (1) of FIG.8.

Since writing of the pixels in the first column from the right of eachsub-irradiation region 29 has been completed, in a next tracking cycleafter resetting the tracking, the deflector 209 performs deflection suchthat the writing position of each corresponding beam is adjusted(shifted) to the second pixel from the right in the first row from thebottom of each sub-irradiation region 29.

As described above, each shot is performed while shifting one controlgrid 27 (pixel 36) by one control grid 27 (pixel 36) by the deflector209, in a state where the relative position of the irradiation region 34to the target object 101 is controlled by the deflector 208 to be anunchanged position during the same tracking cycle. Then, after finishingone tracking cycle and returning the tracking position of theirradiation region 34, as shown in the lower part of FIG. 6, the shotposition for the first shot is adjusted to the position shifted by onecontrol grid (one pixel), for example, and each shot is performedshifting one control grid (one pixel) by one control grid (one pixel) bythe deflector 209 while performing a next tracking control. By repeatingthis operation during writing the stripe region 32, the position of theirradiation region 34 is shifted one by one, such as from 34 a to 34 o,to perform writing of the stripe region concerned.

When writing the target object 101 with the multiple beams 20, asdescribed above, irradiation is performed per control grid (one pixel)sequentially and continuously with multiple beams 20, serving as shotbeams, by moving the beam deflection position by the deflector 209 whilefollowing the movement of the XY stage 105 during the tracking operationby the deflector 208. It is determined, based on the writing sequence,which beam of multiple beams irradiates which control grid 27 (pixel 36)on the target object 101. Then, the region obtained by multiplying thebeam pitch (x direction) by the beam pitch (y direction), where the beampitch is between beams adjacent in the x or y direction of multiplebeams on the surface of the target object 101, is configured by a region(sub-irradiation region 29) composed of n×n pixels. For example, whenthe XY stage 105 moves in the −x direction by the distance of the beampitch (x direction) by one tracking operation, as described above, ncontrol grids (n pixels) are written in the y direction by one beamwhile the irradiation position is shifted. Alternatively, n controlgrids (n pixels) may be written in the x direction or diagonal directionby one beam while the irradiation position is shifted. Then, by the nexttracking operation, other n pixels in the same n×n pixel region aresimilarly written by a different beam from the one used above. Thus, npixels are written each time of n times of tracking operations, using adifferent beam each time, thereby writing all the pixels in one regionof n×n pixels. With respect also to other regions each composed of n×npixels in the irradiation region of multiple beams, the same operationis executed at the same time so as to perform writing similarly.

Next, operations of the writing mechanism 150 of the writing apparatus100 will be described. The electron beam 200 emitted from the electrongun 201 (emission source) almost perpendicularly (e.g., vertically)illuminates the whole of the shaping aperture array substrate 203 by theillumination lens 202. A plurality of quadrangular holes (openings) areformed in the shaping aperture array substrate 203. The region includingall the plurality of holes is irradiated with the electron beam 200. Forexample, a plurality of quadrangular electron beams (multiple beams) 20a to 20 e are formed by letting portions of the electron beam 200, whichirradiates the positions of a plurality of holes, individually passthrough a corresponding hole of the plurality of holes of the shapingaperture array substrate 203. The multiple beams 20 a to 20 eindividually pass through corresponding blankers (first deflector:individual blanking mechanism) of the blanking aperture array mechanism204. Each blanker deflects (provides blanking deflection) the electronbeam 20 which is individually passing.

The multiple beams 20 a to 20 e having passed through the blankingaperture array mechanism 204 are reduced by the reducing lens 205, andgo toward the hole in the center of the limiting aperture substrate 206.At this stage, the electron beam 20 a which was deflected by the blankerof the blanking aperture array mechanism 204 deviates (shifts) from thehole in the center of the limiting aperture substrate 206 and is blockedby the limiting aperture substrate 206. On the other hand, the electronbeams 20 b to 20 e which were not deflected by the blanker of theblanking aperture array mechanism 204 pass through the hole in thecenter of the limiting aperture substrate 206 as shown in FIG. 1.Blanking control is provided by ON/OFF of the individual blankingmechanism so as to control ON/OFF of beams. Thus, the limiting aperturesubstrate 206 blocks each beam which was deflected to be in the OFFstate by the individual blanking mechanism 47. Then, for each beam, oneshot beam is formed by a beam which has been made during a period frombecoming beam ON to becoming beam OFF and has passed through thelimiting aperture substrate 206. The multiple beams 20 having passedthrough the limiting aperture substrate 206 are focused by the objectivelens 207 so as to be a pattern image of a desired reduction ratio. Then,respective beams (the whole of the multiple beams 20) having passedthrough the limiting aperture substrate 206 are collectively deflectedin the same direction by the deflectors 208 and 209 in order toirradiate respective beam irradiation positions on the target object101. Ideally, the multiple beams 20 irradiating at a time are aligned atpitches obtained by multiplying the arrangement pitch of a plurality ofholes of the shaping aperture array substrate 203 by a desired reductionratio described above.

FIG. 9 is a flowchart showing main steps of a writing method accordingto the first embodiment. In FIG. 9, the writing method of the firstembodiment executes a series of steps: an area ratio map generation step(S102), a dose map generation step (S104) per stripe, abeam-positional-deviation-amount measurement step (S112), abeam-positional-deviation-amount map generation step (S114) per beamarray, a beam-positional- deviation-amount map generation step (S116)per stripe, a dose distribution table generation step (S118), a dose mapcorrection step (S130) per stripe, and a writing step (S140).

In the area ratio map generation step (rasterizing step) (S102), therasterizing unit 50 reads writing data from the storage device 140, andcalculates, for each pixel 36, a pattern area density p′ in the pixel 36concerned. This processing is performed for each stripe region 32, forexample.

In the dose map generation step (S104) per stripe, first, the dose mapgeneration unit 52 virtually divides the writing region (here, forexample, stripe region 32) into a plurality of proximity mesh regions(mesh regions for proximity effect correction calculation) by apredetermined size. The size of the proximity mesh region is preferablyabout 1/10 of the influence range of the proximity effect, such as about1 μm. The dose map generation unit 52 reads writing data from thestorage device 140, and calculates, for each proximity mesh region, apattern area density p of a pattern arranged in the proximity meshregion concerned.

Next, the dose map generation unit 52 calculates, for each proximitymesh region, a proximity-effect correction irradiation coefficientD_(p)(x) (correction dose) for correcting a proximity effect. An unknownproximity-effect correction irradiation coefficient Dp(x) can be definedby a threshold value model for proximity-effect correction, which is thesame as the one used in a conventional method, where a backscattercoefficient η, a dose threshold value Dth of a threshold value model, apattern area density ρ, and a distribution function g(x) are used.

Next, the dose map generation unit 52 calculates, for each pixel 36, anincident dose D(x) (dose) with which the pixel 36 concerned isirradiated. The incident dose D(x) can be calculated, for example, bymultiplying a pre-set base dose D_(base), a proximity effect correctionirradiation coefficient D_(p), and a pattern area density ρ′. The basedose D_(base) can be defined by Dth/(½+η), for example. Thereby, it ispossible to obtain an originally desired incident dose D(x), for whichthe proximity effect has been corrected, based on layout of a pluralityof figure patterns defined by the writing data.

The dose map generation unit 52 generates, per stripe, a dose map whichdefines an incident dose D(x) for each pixel 36. The incident dose D(x)for each pixel 36 is an incident dose D(x) planned in design toirradiate the control grid 27 of the pixel 36 concerned. In other words,the dose map generation unit 52 generates a dose map (1) which defines,per stripe, the incident dose D(x) for each control grid 27. Thegenerated dose map (1) is stored in the storage device 142, for example.

In the beam-positional-deviation-amount measurement step (S112), thewriting apparatus 100 measures an amount of positional deviation fromthe control grid 27 corresponding to each beam of the multiple beams 20.

FIGS. 10A and 10B illustrate a beam positional deviation and apositional deviation periodicity according to the first embodiment. Inthe multiple beams 20, as shown in FIG. 10A, distortion occurs in anexposure field due to optical system characteristics, and therefore, anactual irradiation position 39 of each beam deviates from an irradiationposition 37 of the ideal grid because of the distortion. Then, in thefirst embodiment, the amount of positional deviation of the actualirradiation position 39 of each beam is measured. Specifically, anevaluation substrate coated with resist is irradiated with the multiplebeams 20, and the irradiated evaluation substrate is developed in orderto generate a resist pattern. Then, the position of the generated resistpattern is measured by a position measuring instrument so as to measurea positional deviation amount of each beam. If it is difficult tomeasure the size of the resist pattern at the irradiation position ofeach beam by a position measuring instrument since the shot size of thebeam concerned is small, it should perform to write a figure pattern(e.g., rectangular pattern) of measurable size by a position measuringinstrument, measure edge positions of the both sides of the figurepattern (resist pattern), and measure a positional deviation amount of atarget beam based on a difference between the intermediate positionbetween the both edges and the intermediate position of a figure patternin design. Then, data of an obtained positional deviation amount on theirradiation position of each beam is input into the writing apparatus100, and stored in the storage device 144. Moreover, in the multi-beamwriting, in the case of the writing sequence explained in FIG. 8, forexample, since writing proceeds while shifting the irradiation region 34in the stripe region 32, periodicity occurs in positional deviation ofeach beam every time the irradiation region 34 is moved because theposition of the irradiation region 34 moves one by one, such as from theirradiation region 34 a to 34 o, during writing of the stripe region 32as shown in the lower part of FIG. 6. Alternatively, in the case of thewriting sequence where each beam irradiates all the pixels 36 in the subirradiation region 29 corresponding to the beam concerned, as shown inFIG. 10B, periodicity occurs at least in the positional deviation ofeach beam in each unit region 35 (35 a, 35 b, . . . ) having the samesize as the irradiation region 34. Therefore, if the positionaldeviation amount of each beam for one irradiation region 34 is measured,the measurement result can also be used for other regions. In otherwords, it is sufficient to measure a positional deviation amount at eachpixel 36 in the sub irradiation region 29 corresponding to each beam.

In the beam-positional-deviation-amount map generation step (S114) perbeam array, the beam-positional-deviation map generation unit 54generates a beam-positional-deviation-amount map (1) (firstbeam-positional-deviation-amount map) which defines the amount ofpositional deviation of each beam in beam array units, in other words,the irradiation region 34. Specifically, the beam-positional-deviationmap generation unit 54 reads positional deviation amount data on theirradiation position of each beam from the storage device 144, andgenerates the beam-positional-deviation-amount map (1) by using the dataas a map value.

In the beam-positional-deviation-amount map generation step (S116) perstripe, the beam-positional-deviation map generation unit 54 generates abeam-positional-deviation-amount map (2) (secondbeam-positional-deviation-amount map) for the control grid 27 of eachpixel 36 in the stripe region 32. Which beam irradiates the control grid27 of each pixel 36 in the stripe region 32 is determined based on thewriting sequence as shown in FIG. 8, for example. Therefore, for eachcontrol grid 27 of each pixel 36 in the stripe region 32, thebeam-positional-deviation map generation unit 54 specifies a beam toirradiate the control grid 27 concerned according to the writingsequence, and calculates a positional deviation amount of the beamconcerned. The beam-positional-deviation map generation unit 54generates the beam-positional-deviation-amount map (2) for each stripeby using the amount of positional deviation of the irradiation positionof a beam toward each control grid 27, as a map value. As describedabove, since periodicity occurs in the positional deviation of eachbeam, the beam-positional-deviation-amount map (2) for each stripe canbe generated by using the value of the beam-positional-deviation-amountmap (1) for each beam array.

In the dose distribution table generation step (S118), for each controlgrid 27, there is generated a dose distribution table for distributing adose, which is set for the control grid 27 concerned, to surroundingbeams.

FIG. 11 is a flowchart showing an example of internal steps of the dosedistribution table generation step according to the first embodiment. InFIG. 11, the dose distribution table generation step (S118) executes aseries of steps as internal steps: a target grid selection step (S202),a proximity beam search step (S204), a combination setting step (S206),a dose distribution ratio calculation step (S208), a dose distributioncoefficient calculation step (S210), and a dose distribution tablegeneration step (S212).

In the target grid selection step (S202), the selection unit 56 selectsa control grid of interest (target control grid) in a plurality ofcontrol grids 27 in a target stripe region 32.

In the proximity beam search step (S204), for each control grid 27 in aplurality of control grids 27 (design grid) being irradiation positionsin design of the multiple beams 20, the search unit 58 searches for fouror more proximity beams whose actual irradiation positions are close tothe control grid 27 concerned.

FIG. 12 illustrates a method of searching for a proximity beam accordingto the first embodiment. Since a positional deviation occurs in a beamirradiating each control grid 27 as described above, the practicalirradiation position (actual irradiation position) of each beam isdeviated (shifted) from the control grid 27 corresponding to the beamconcerned as shown in FIG. 12 FIG. 12 illustrates a method of searchingfor a proximity beam according to the first embodiment. Therefore, inFIG. 12, a plurality of actual irradiation positions 39 (white) existaround the target control grid 27 (grid of interest) (black) representedby the coordinates d(i, j). It is sufficient that the number ofproximity beams is four or more. In the first embodiment, the case ofsearching for four proximity beams and selecting them will be described.

The search unit 58 (proximity beam selection unit) searches for andselects, for each control grid 27 (design grid), a beam corresponding tothe closest irradiation position in each of four regions obtained bybeing divided by two straight lines which pass the control grid 27concerned and have different angles, as four proximity beams whoseactual irradiation positions are close to the control grid 27 concerned.An actual irradiation position can be acquired based on thebeam-positional-deviation-amount map (2). In the example of FIG. 12, astraight line 43 a parallel to the x-axis and a straight line 43 bparallel to the y-axis, which are passing the target control grid 27(grid of interest) represented by the coordinates d(i, j), are used asthe two straight lines having different angles. In other words, thex-axis and the y-axis centering on a target grid are set. The regionaround the target grid is divided into four regions (first to fourthquadrants) by the x-axis and the y-axis. Then, the search unit 58(proximity beam selection unit) selects a beam corresponding to theclosest irradiation position 39 b in the first quadrant (A), a beamcorresponding to the closest irradiation position 39 a in the secondquadrant (B), a beam corresponding to the closest irradiation position39 c in the third quadrant (C), and a beam corresponding to the closestirradiation position 39 d in the fourth quadrant (D).

FIG. 13 shows an example of a control grid and an actual irradiationposition of each beam according to the first embodiment. FIG. 13 showsthe case (U) where the actual irradiation position 39 of a beamcorresponding to the target control grid 27 (control grid of interest)located in the center deviates to the upper left side (−x and +ydirection). Moreover, FIG. 13 shows the case (V) where the actualirradiation position 39 of a beam corresponding to a control gridadjacent in the −x direction to the target control grid 27 deviates tothe lower right side (+x and −y direction). Moreover, FIG. 13 shows thecase (W) where the actual irradiation position 39 of a beamcorresponding to a control grid adjacent in the +x direction to thetarget control grid 27 deviates to the lower left side (−x and −ydirection). Moreover, FIG. 13 shows the case (Z) where the actualirradiation position 39 of a beam corresponding to a control gridadjacent but one in the +y direction to the target control grid 27deviates by a longer distance than the control grid pitch size to thelower right side (+x and −y direction). As described in the example ofFIG. 13, the direction of positional deviation of a beam correspondingto each control grid 27 (black) is not necessarily the same. Moreover,the actual irradiation position 39 (white) of a beam corresponding toeach control grid 27 (black) does not necessarily exist between a targetgrid and a control grid adjacent to the target grid. Positionaldeviation may occur at the position farther than the distance of thecontrol grid pitch size. It is sufficient for the search unit 58 toselect a beam whose actual irradiation position 39 is closest in eachquadrant, independent of the correspondence relation between the controlgrid 27 and the beam.

In the combination setting step (S206), for each of a plurality ofcontrol grids 27 being irradiation positions in design of the multiplebeams 20, the combination setting unit 60 sets a plurality ofcombinations 42 a and 41 b each composed of three beams whose actualirradiation positions 39 surround the control grid 27 concerned, byusing four or more beams whose actual irradiation positions 39 are closeto the control grid 27 concerned. In the example of FIG. 12, onecombination 42 a is set using three proximity beams of a beamcorresponding to the closest irradiation position 39 b in the firstquadrant (A), a beam corresponding to the closest irradiation position39 a in the second quadrant (B), and a beam corresponding to the closestirradiation position 39 c in the third quadrant (C). Another combination42 b is set using three proximity beams of a beam corresponding to theclosest irradiation position 39 a in the second quadrant (B), a beamcorresponding to the closest irradiation position 39 c in the thirdquadrant (C), and a beam corresponding to the closest irradiationposition 39 d in the fourth quadrant (D). When selecting one proximitybeam from each quadrant in order to surround the target control grid 27(grid of interest), usually, there are two combinations.

In the dose distribution ratio calculation step (S208), the dosedistribution ratio calculation unit 62 (first distribution coefficientcalculation unit) calculates, for each of a plurality of combinations, adistribution ratio w_(k)′ (first distribution coefficient) for each ofthree beams configuring the combination concerned, for distributing adose to irradiate the control grid 27 concerned to the three beamsconfiguring the combination concerned, such that the position of thegravity center of each distributed dose coincides with the position ofthe control grid 27 concerned and the sum of each distributed dose afterdistribution coincides with the dose to irradiate the control grid 27concerned.

FIGS. 14A to 14D illustrate a method for distributing a dose tosurrounding three proximity beams according to the first embodiment.FIG. 14A shows actual irradiation positions 39 (white) of three beams toirradiate the periphery of the target grid (control grid 27) (black).The coordinates of the irradiation positions 39 of the three beams are(x₁, y₁), (x₂, y₂), and (x₃, y₃). When representing the coordinates ofthe irradiation positions 39 of the three beams by using relativepositions whose origin is the coordinates (x, y) of the target grid(control grid 27), the relative coordinates are (Ax₁, Ay₁), (Ax₂, Ay₂),and (Ax₃, Ay₃). When distributing the dose d to irradiate the targetgrid (control grid 27) of the coordinates (x, y) to the three beams, formaking the position of the gravity center of each of doses d₁, d₂, andd₃ (distributed dose) after distribution be the coordinates (x, y), andmaking the sum of each of the doses d₁, d₂, and d₃ (distributed dose)after distribution be the dose d, the determinant shown in FIG. 14Bshould be satisfied. In other words, each of the doses d1, d2, and d3after distribution is determined to satisfy the following equations (1)to (3).

x ₁ ·d ₁ +x ₂ ·d ₂ +x ₃ ·d ₃ =x   (1)

y ₁ ·d ₁ +y ₂ ·d ₂ +y ₃ ·d ₃ =y   (2)

d ₁ +d ₂ +d ₃ =d   (3)

Therefore, each of the doses d₁, d₂, and d₃ (distributed dose) afterdistribution can be calculated from the determinant shown in FIG. 14C.In other words, each dose d_(k) after distribution (that is, distributeddose) can be defined by multiplying the dose d to irradiate a targetgrid (control grid 27) by the distribution ratio w_(k)′ shown in FIG.14D. Accordingly, the distribution ratio w_(k)′ for each of three beamsaround a target grid (control grid 27) (black) can be obtained by thecalculation of FIG. 14C. In other words, the distribution ratio w_(k)!for each of three beams satisfies the following equations (4) to (7).

d ₁ =w ₁ ′·d   (4)

d ₂ =w ₂ ′·d   (5)

d ₃ =w ₃ ′·d   (6)

w ₁ ′+w ₂ ′+w ₃′=1   (7)

In the dose distribution coefficient calculation step (S210), the dosedistribution coefficient calculation unit 64 (second distributioncoefficient calculation unit) calculates, for each of four or more beams(here, e.g., four beams), a distribution coefficient w_(k) (seconddistribution coefficient) of each of four or more beams (here, e.g.,four beams) relating to the control grid 27 (design grid) concerned bydividing the total of distribution ratios w_(k)′ (first distributioncoefficient) corresponding to the beam concerned by the number of aplurality of combinations. At the stage of the dose distribution ratiocalculation step (S208), only a distribution ratio w_(k)′ for each ofthree beams configuring the combination concerned has been calculatedfor each combination. However, with respect to a target grid (controlgrid 27) (black), a plurality of combinations exist in which a beam isused for not only for one combination but also for another combination.Therefore, two of four beams obtained from the four quadrants are usedfor configuring two combinations, for example. In the case of FIG. 12,the beam at the irradiation position 39 a is used for the combinations42 a and 42 b. Similarly, the beam at the irradiation position 39 c isused for the combinations 42 a and 42 b. Thus, with respect to the beamsat the irradiation positions 39 a and 39 c, the distribution ratiow_(k)′ in the case of the combination 42 a and the distribution ratiow_(k)′ in the case of the combination 42 b are individually calculated.On the other hand, the beam at the irradiation position 39 b is used forthe combination 42 a, but not for the combination 42 b. Therefore, withrespect to the beam at the irradiation position 39 b, the distributionratio w_(k)′ in the case of the combination 42 a is calculated, but thatin the case of the combination 42 b is not calculated. In contrast, thebeam at the irradiation position of 39 d is used for the combination 42b, but not for the combination 42 a. Thus, with respect to the beam atthe irradiation position of 39 d, the distribution ratio w_(k)′ in thecase of the combination 42 b is calculated, but that in the case of thecombination 42 a is not calculated. The total of distribution ratiosw_(k)′ calculated for four beams selected for a target grid (controlgrid 27) (black) is “2” being the same number as that of thecombinations. Then, the dose distributed according to combination isdetermined to be (1/number of combinations). Based on this calculation,the distribution coefficient w_(k) for each beam, based on which thedose d to irradiate the control grid 27 concerned is distributed intofour selected beams, is obtained for each target grid (control grid 27)(black).

In the dose distribution table generation step (S212), the dosedistribution table generation unit 66 generates a dose distributiontable in which the distribution coefficients w_(k) for four beamscalculated for each target grid (control grid 27) (black) are definedrelating to the target grids (control grids 27).

FIG. 15 shows an example of a dose distribution table according to thefirst embodiment. In the case of FIG. 15, identification coordinates(i_(k), j_(k)) of four beams being distribution destinations, anddistribution coefficients w_(k) for the four beams serving as thedistribution destinations are defined for each target grid (control grid27) (black) of coordinates (i, j).

After a dose distribution table has been generated for one target grid(control grid 27) (black), each step from the target grid selection step(S202) to the dose distribution table generation step (S212) isrepeated, regarding a next control grid 27 as a target grid in order,until dose distribution tables have been generated for all the controlgrids in the stripe region concerned.

In the dose map correction step (S130) per stripe, the dose modulationunit 68 first reads a dose map (1), generated in the dose map generationstep (S104) per stripe and defining the incident dose D for each controlgrid 27, from the storage device 142. Then, using the dose distributiontable, the dose modulation unit 68 distributes a distribution dose,obtained by multiplying the incident dose D for the control grid 27concerned by a calculated distribution coefficient w_(k) of each of fourbeams serving as destinations of distribution, to each control grid 27where irradiation positions in design of the four beams are respectivedestinations of the distribution. The dose modulation unit 68 correctsthe incident dose D for each control grid 27 in the dose map byperforming modulation by the distribution described above, and generatesa modulated dose map (2) after correction. Preferably, the dosemodulation unit 68 converts the modulated incident dose D aftercorrection for each control grid 27 into an irradiation time t which hasbeen graded by gray scale levels using a predetermined quantization unitΔ in order to define the irradiation time t in the modulated dose map(2).

In the writing step (S140), the writing mechanism 150 writes a patternon the target object 101 with the multiple beams 20 in which the dose dto irradiate each control grid 27 (design grid) has been distributed toeach corresponding one of four or more beams. Specifically, it operatesas described below. The irradiation time t of a beam to each controlgrid 27 of the stripe region 32 to be written is defined in themodulated dose map (2). The writing control unit 72 rearrangesirradiation time t data defined in the modulated dose map (2) in orderof shot in accordance with the writing sequence. Then, the writingcontrol unit 72 transmits the irradiation time t data to the deflectioncontrol circuit 130 in order of shot. The deflection control circuit 130outputs a blanking control signal to the blanking aperture arraymechanism 204 in order of shot, and a deflection control signal to theDAC amplifier units 132 and 134 in order of shot. The writing mechanism150, as described above, performs writing on the target object 101 withthe multiple beams 20 such that each control grid 27 is irradiated.Actually, although the irradiation position 39 of the beam to irradiateeach control grid 27 deviates from the control grid 27 in design asdescribed above, since dose modulation has been performed, positionaldeviation of a pattern formed on the resist pattern formed afterexposure can be corrected.

FIGS. 16A and 16B show examples of a dose frequency based on dosedistribution according to the first embodiment. FIGS. 16A and 16B showexamples of dose frequencies of all the shots of the multiple beams 20to write the stripe region 32. When not distributing the dose tosurrounding beams, the level of an incident dose (dose amount) toirradiate each control grid 27 (irradiation position) in the case ofperforming dose modulation needs to be, for example, several hundredpercent of that of the base dose as described above. Therefore, themaximum irradiation time becomes further increased. In contrast, whendistributing the incident dose (dose amount) to irradiate the controlgrid 27 to surrounding three beams, the maximum dose can be reduced tothe value of 1.8 times the base dose as shown in the example of FIG.16A. When distributing the incident dose (dose amount) to irradiate thecontrol grid 27 to surrounding four beams as described in the firstembodiment, the maximum dose can be further reduced to the value of 1.4times the base dose as shown in the example of FIG. 16B. If distributingsuch a dose to four or more beams, the maximum dose may further bereduced. In other words, the maximum irradiation time in all the shotsof the multiple beams 20 can be greatly reduced.

Further, when distributing the incident dose (dose amount) to irradiatethe control grid 27 to surrounding three beams, the value of dispersionof 3σ at the pattern edge to be written is 1.34 nm as shown in theexample of FIG. 16A. In contrast, when distributing the incident dose(dose amount) to irradiate the control grid 27 to surrounding four beamsas described in the first embodiment, the value of dispersion of 3G atthe pattern edge to be written can be reduced to 1.08 nm as shown in theexample of FIG. 16B, thereby also having a great effect of reducing theamount of positional deviation.

As described above, according to the first embodiment, it is possible toreduce the adjustment width of dose modulation in multi-beam writing.Accordingly, the maximum irradiation time can be shortened. Therefore,the throughput can be improved.

Second Embodiment

In the above first embodiment, the case has been described where theadjustment width of dose modulation is reduced premising to correctpositional deviation occurring in a pattern to be written caused bypositional deviation of the irradiation position. In a secondembodiment, there will be described a configuration in which theadjustment width of dose modulation can be reduced further than that ofthe first embodiment in order to improve the throughput even at the costof some correction effects for positional deviation occurring in apattern.

FIG. 17 is a conceptual diagram showing a configuration of a writingapparatus according to the second embodiment. FIG. 17 is the same asFIG. 1 except that, in the control computer 110, a specifying unit 73, asearch unit 74, a setting unit 75, a redistribution unit 76, a gravitycenter calculation unit 77, a selection unit 78, a correction unit 79,and a dose map generation unit 90 are further arranged. Therefore, eachof “ . . . units” such as the rasterizing unit 50, the dose mapgeneration unit 52, the beam-positional-deviation map generation unit54, the selection unit 56, the search unit 58, the combination settingunit 60, the dose distribution ratio calculation unit 62, the dosedistribution coefficient calculation unit 64, the dose distributiontable generation unit 66, the dose modulation unit 68, the writingcontrol unit 72, the specifying unit 73, the search unit 74, the settingunit 75, the redistribution unit 76, the gravity center calculation unit77, the selection unit 78, the correction unit 79, and the dose mapgeneration unit 90 includes a processing circuitry. As the processingcircuitry, for example, an electric circuit, computer, processor,circuit board, quantum circuit, or semiconductor device is used. Each “. . . unit” may use a common processing circuitry (same processingcircuitry), or different processing circuitries (separate processingcircuitries). Information input and output to/from each of theabove-described units, and information being operated are stored in thememory 112 each time.

FIG. 18 is a flowchart showing main steps of a writing method accordingto the second embodiment. FIG. 18 is the same as FIG. 9 except that adose distribution table adjustment step (S120) is added between the dosedistribution table generation step (S118) and the dose map correctionstep (S130) per stripe. The contents of the second embodiment are thesame as those of the first embodiment except for what is specificallydescribed below.

The contents of each of the area ratio map generation step (S102), thedose map generation step (S104) per stripe, thebeam-positional-deviation-amount measurement step (S112), thebeam-positional-deviation-amount map generation step (S114) per beamarray, the beam-positional-deviation-amount map generation step (S116)per stripe, and the dose distribution table generation step (S118) arethe same as those of the first embodiment.

In the dose distribution table adjustment step (S120), the generateddose distribution table is adjusted in order to partially correct themethod for distributing the dose.

FIG. 19 is a flowchart showing internal steps in the dose distributiontable adjustment step according to the second embodiment. In FIG. 19,the dose distribution table adjustment step (S120) executes a series ofsteps as its internal steps: a dose map generation step (S220), a beamspecifying step (S222), a proximity beam search step (S224), acombination setting step (S226), a dose redistribution step (S228), agravity center calculation step (S230), a combination selection step(S232), and a dose distribution table correction step (S234).

In the dose map generation step (S220), using the generated dosedistribution table, when the incident dose D in the case of the areadensity of uniformly 100% is defined in all the control grids 27 of thestripe region 32 to be written, the dose map generation unit 90distributes a distribution dose, obtained by multiplying the incidentdose D for the control grid 27 concerned by a calculated distributioncoefficient w_(k) of each of four beams serving as destinations ofdistribution, to each control grid 27 where irradiation positions indesign of the four beams are respective destinations of thedistribution. Then, the dose map generation unit 90 corrects theincident dose D for each control grid 27 in the dose map by performingan adjustment by the distribution described above, and generates anmodulated dose map (3) after correction. The incident dose D in the caseof the area density of uniformly 100% may also be a standardized value“1”, for example. In such a case, the dose of each control grid 27 afterthe adjustment is the total of distribution coefficients w_(k)distributed from the surrounding control grids 27. The generated dosemap (3) is stored in the storage device 142, for example.

In the beam specifying step (S222), the specifying unit 73 reads thedose map (3) from the storage device 142, and specifies a beam whoseamount of distributed dose exceeds a pre-set threshold.

FIG. 20 shows an example of a dose map in the case of assuming the areadensity of uniformly 100% according to the second embodiment. FIG. 20shows 10×10 control grids (black spots), and actual irradiationpositions (cross marks) of 10×10 beams irradiating the 10×10 controlgrids, for example. The difference in the size of circles at the actualirradiation positions (cross marks) indicates a difference in the amountof doses. In the example of FIG. 20, a larger circle indicates a largerdose amount. As shown in the case of FIG. 20, it turns out that,depending on the amount of beam positional deviation, there are beams ofa large amount of dose and a small amount of dose after dosedistribution. Therefore, it turns out that there is still more room toreduce the adjustment width of dose modulation as long as making thecorrection effect for a positional deviation amount be somewhatsacrificed.

In the proximity beam search step (S224), with respect to specifiedbeams each of whose distributed dose amount d exceeds a threshold Th′,the search unit 74 searches for a plurality of proximity beams close tothe periphery of the beam concerned, for each specified beam.

FIG. 21 illustrates a method of searching for a proximity beam close toa specific beam whose distributed dose amount exceeds a thresholdaccording to the second embodiment. The search unit 74 searches for andselects beams corresponding to a plurality of irradiation positionswhich receive dose distribution from four control grids 27 a to 27 dsurrounding the irradiation position (here, irradiation position 39 c)of the specific beam 45 concerned. Specifically, with respect to thefour control grids 27 a to 27 d surrounding the irradiation position(here, irradiation position 39 c) of the specific beam 45 concerned, thesearch unit 74 reads a generated dose distribution table from thestorage device 142 for each of the control grids 27 a to 27 d, andsearches for and selects beams corresponding to, for example, fourirradiation positions to which a dose is distributed from the controlgrid 27 concerned. By this operation, in the example of FIG. 21, thesearch unit 74 specifies beams 46 a, 46 b, and 46 g, in addition to thespecific beam 45 concerned, to which a dose will be distributed from thecontrol grid 27 a. Moreover, the search unit 74 specifies beams 46 a, 46d, and 46 c, in addition to the specific beam 45 concerned, to which adose will be distributed from the control grid 27 b. Moreover, thesearch unit 74 specifies beams 46 c, 46 e, and 46 f, in addition to thespecific beam 45 concerned, to which a dose will be distributed from thecontrol grid 27 c.

Moreover, the search unit 74 specifies beams 46 f, 46 h, and 46 g, inaddition to the specific beam 45 concerned, to which a dose will bedistributed from the control grid 27 d. As described above, the searchunit 74 specifies and selects, for example, eight beams 46 a to 46 haround the specific beam 45 concerned. In many cases, a plurality ofspecified beams other than the specific beam 45 concerned areoverlappingly selected with respect to each of the control grids 27 a to27 d. By using a generated dose distribution table, the search unit 74can easily specify, for example, the eight beams 46 a to 46 h around thespecific beam 45 concerned.

Now, in the case of redistributing a dose exceeding the threshold, thefollowing method can be used as a simple method. By using generated dosedistribution tables for four control grid 27 a to 27 d in which thespecific beam 45 concerned is defined as a distribution destination, anyone of the four control grids 27 a to 27 d is selected. Then, withrespect to four beams defined as distribution destinations of theselected control grid 27, redistribution is performed to the remainingbeams other than the specific beam 45 concerned. Specifically, itoperates as described below.

In the combination setting step (S226), the setting unit 75 sets aplurality of combinations each of which is composed of the specific beam45 concerned and the remaining three beams defined in the generated dosedistribution table for each of the control grids 27 a to 27 d. In otherwords, the combination is set for each dose distribution table.

In the dose redistribution step (S228), first, the writing control unit72 calculates, for each specified beam, a difference dose d′ forredistribution by subtracting a threshold dth from a distribution dose dof the specific beam 45 concerned. Since the distribution dose d (thetotal of doses distributed from surrounding control grids 27) of thespecific beam 45 concerned and the distribution dose d (the total ofdoses distributed from surrounding control grids 27) of each of thesurrounding eight beams 46 a to 46 h, for example, have already beencalculated in the dose map generation step (S220), these values can beused in the present step. Next, for each combination, until thedifference dose d′ becomes zero, the redistribution unit 76 assigns aportion of the difference dose d′, as a redistribution dose, to each ofthree beams other than the specific beam 45 concerned in four beams ofthe combination concerned in the order of distribution dose amount fromsmallest to largest until reaching respective thresholds dth.Alternatively, it is also preferable that the redistribution unit 76assigns, for each combination, a dose equivalent to redistribution dosed′/J, obtained by dividing the difference dose d′ by J being the numberof beams (in this case, three) other than the specific beam 45 concernedfor the combination concerned, uniformly to each of the J beams.

In the gravity center calculation step (S230), the gravity centercalculation unit 77 calculates, for each combination, the position ofthe gravity center of each distribution dose of four beams, for example,defined in the dose distribution table after redistribution to eachbeam.

In the combination selection step (S232), the selection unit 78(redistribution beam selection unit) selects, as a plurality ofproximity beams serving as redistribution destinations, a proximity beamcombination with respect to which deviation of the position of thegravity center due to redistribution is least, from a plurality ofcombinations. Specifically, it operates as described below. Theselection unit 78 selects a combination with respect to which theposition of the gravity center of each distribution dose afterredistribution deviates least from the control grid 27 corresponding tothe combination concerned. In many cases, there are four dosedistribution tables defining the specific beam 45 concerned as adistribution destination. Therefore, in the combination selection step(S232), a dose distribution table with respect to which the gravitycenter deviates least in the case of dose redistribution is selectedfrom the four dose distribution tables.

In the dose distribution table correction step (S234), the correctionunit 79 corrects the distribution coefficient w_(k) of each of fourbeams defined in the dose distribution table of a selected combination.

FIG. 22 shows an example of a dose distribution table after correctionaccording to the second embodiment. In FIG. 22, for each target grid(control grid 27) (black) of the coordinates (i, j) corresponding to aselected combination, the distribution coefficient w_(k) for each offour beams of identification coordinates (i_(k), j_(k)) being adistribution destination is corrected to a distribution coefficientw_(k)′. Specifically, a coefficient A for the dose to be redistributedis added to the distribution coefficient w_(k) of each of three beamswhich receive redistribution, for example. The distribution coefficientof the specific beam whose distributed dose amount exceeds a thresholdis corrected by multiplying by a value, as a coefficient, obtained bydividing the threshold dth by a distribution dose d of the specific beam45 exceeding the threshold. This corrects the dose distribution table ofthe selected combination.

Alternatively, as a modified example, it is also preferable to performdose redistribution regardless of combination of each dose distributiontable. In that case, it operates as described below.

In the combination setting step (S226), the setting unit 75 sets aplurality of combinations each composed of pre-set J beams out ofsearched m proximity beams. In the example of FIG. 21, since the eightproximity beams 46 a to 46 h around the specific beam 45 concerned havealready been searched, a plurality of combinations each composed of, forexample, five proximity beams are randomly set out of the eightproximity beams 46 a to 46 h. It is preferable to acquire a plurality ofcombinations by selecting J proximity beams from the m proximity beamsby a round robin method.

In the dose redistribution step (S228), first, the writing control unit72 calculates, for each specified beam, a difference dose d′ forredistribution by subtracting the threshold dth from a distribution dosed of the specific beam 45 concerned. Since the distribution dose d (thetotal of doses distributed from surrounding control grids 27) of thespecific beam 45 concerned and the distribution dose d (the total ofdoses distributed from surrounding control grids 27) of each of thesurrounding eight proximity beams 46 a to 46 h, for example, havealready been calculated in the dose map generation step (S220), thesevalues can be used in the present step. Next, for each combination,until the difference dose d′ becomes zero, the redistribution unit 76assigns a portion of the difference dose d′, as a redistribution dose,in the order of distribution dose amount from smallest to largest withrespect to J proximity beams of the combination concerned until reachingrespective thresholds dth.

Alternatively, it is also preferable that the redistribution unit 76uniformly assigns, for each combination,_a dose equivalent toredistribution dose d′/J, obtained by dividing the difference dose d′ byJ being the number of beams, to each of the J proximity beams of thecombination concerned. Here, since J being the number of beamsconfiguring a combination can be set arbitrarily, generation ofredistribution remnants of the difference dose d′ can be substantiallyavoided.

In the gravity center calculation step (S230), the gravity centercalculation unit 77 calculates, for each combination, the position ofthe gravity center of a dose to be redistributed to each proximity beam.

In the combination selection step (S232), the selection unit 78(redistribution beam selection unit) selects, as a plurality ofproximity beams serving as redistribution destinations, a proximity beamcombination with respect to which deviation of the position of thegravity center due to redistribution is least, from a plurality ofcombinations. Specifically, it operates as described below. Theselection unit 78 selects, as a J (plural) proximity beams serving asredistribution destinations, a proximity beam combination (composed of Jbeams) with respect to which the position of the gravity center of eachredistribution dose (a portion of distribution dose of a specific beamwhose distribution dose exceeds a threshold) to be redistributeddeviates least from the irradiation position (e.g., irradiation position39 c) of the specific beam 45 concerned.

In the dose distribution table correction step (S234), for each beam ofa selected proximity beam combination (composed of J beams), thecorrection unit 79 reads a plurality of dose distribution tables inwhich the beam concerned is defined as a distribution destination, andperforms correction such that a redistribution coefficient Δ obtained bydividing a coefficient equivalent to a redistribution dose to beredistributed by the number of distribution destinations is added to theoriginal distribution coefficient defined in each dose distributiontable. For example, if the coefficient equivalent to a redistributiondose to be redistributed to one of selected proximity beam combinationsis 0.4, and the number of dose distribution tables of a distributiondestination is four, 0.1 should be added to each corresponding dosedistribution table.

Moreover, with respect to a distribution coefficient of a specific beamwhose distribution dose exceeds a threshold, the correction unit 79reads a dose distribution table defining a selected proximity beamcombination (composed of J beams), and then, the distributioncoefficient of the specific beam in each dose distribution table ismultiplied by a value, as a coefficient, obtained by dividing thethreshold dth by a distribution dose d of the specific beam 45 exceedingthe threshold. This corrects each dose distribution table relevant to aselected proximity beam combination.

The contents of each step after the dose map correction step (S130) perstripe are the same as those of the first embodiment.

According to the second embodiment, since redistribution is performedwhile shifting the position of the center of gravity for a portion ofthe dose which has originally been distributed with consideration fornot changing the position of the center of gravity, positional deviationcan be as small as possible even though it occurs a little.

According to the second embodiment, the adjustment width of dosemodulation can be reduced much more than that of the first embodiment,thereby further improving the throughput.

Third Embodiment

In the above second embodiment, the case has been described where a dosedistribution table is corrected before adjusting a dose corresponding toan actual writing pattern, but the method of reducing the adjustmentwidth of dose modulation is not limited thereto. In a third embodiment,there will be described a method of further reducing the adjustmentwidth of dose modulation after modulating the dose corresponding to anactual writing pattern by using a dose distribution table.

FIG. 23 is a conceptual diagram showing a configuration of a writingapparatus according to the third embodiment. FIG. 23 is the same as FIG.1 except that, in the control computer 110, a specifying unit 80, asearch unit 81, a setting unit 82, a redistribution unit 83, a gravitycenter calculation unit 84, a selection unit 85, and a modulating unit86 are further arranged. Therefore, each of “ . . . units” such as therasterizing unit 50, the dose map generation unit 52, thebeam-positional-deviation map generation unit 54, the selection unit 56,the search unit 58, the combination setting unit 60, the dosedistribution ratio calculation unit 62, the dose distributioncoefficient calculation unit 64, the dose distribution table generationunit 66, the dose modulation unit 68, the writing control unit 72, thespecifying unit 80, the search unit 81, the setting unit 82, theredistribution unit 83, the gravity center calculation unit 84, theselection unit 85, and the modulating unit 86 includes a processingcircuitry. As the processing circuitry, for example, an electriccircuit, computer, processor, circuit board, quantum circuit, orsemiconductor device is used. Each “ . . . unit” may use a commonprocessing circuitry (same processing circuitry), or differentprocessing circuitries (separate processing circuitries). Informationinput and output to/from each of the above-described units, andinformation being operated are stored in the memory 112 each time.

FIG. 24 is a flowchart showing main steps of a writing method accordingto the third embodiment. FIG. 24 is the same as FIG. 9 except that adose modulation step (S132) is added between the dose map correctionstep (S130) per stripe and the writing step (S140). The contents of thethird embodiment are the same as those of the first embodiment exceptfor what is specifically described below.

The contents of each of the area ratio map generation step (S102), thedose map generation step (S104) per stripe, thebeam-positional-deviation-amount measurement step (S112), thebeam-positional-deviation-amount map generation step (S114) per beamarray, the beam-positional-deviation-amount map generation step (S116)per stripe, the dose distribution table generation step (S118) and thedose map correction step (S130) are the same as those of the firstembodiment.

In the dose modulation step (S132), a generated dose map (2) is adjustedin order to correct a part of the dose distribution method.Specifically, it operates as described below.

The specifying unit 80 reads a dose map (2) from the storage device 142,and specifies a beam (control grid 27) whose incident dose D (doseamount) exceeds a pre-set threshold Dth.

Next, for each specified beam whose incident dose D (dose amount)exceeds the threshold Dth, the search unit 81 searches for a pluralityof proximity beams close to the periphery of the beam concerned.Specifically, it operates as described below. The search unit 81searches for a plurality of proximity beams around the specific beam 45whose actual irradiation position (e.g., irradiation position 39 c) isthe control grid 27 whose incident dose D (dose amount) exceeds thethreshold Dth. According to the third embodiment, similarly to thesecond embodiment, the search unit 81 searches for and selects beamscorresponding to a plurality of irradiation positions which receive dosedistribution from four control grids 27 a to 27 d surrounding theirradiation position (here, irradiation position 39 c) of the specificbeam 45 concerned.

According to the third embodiment, similarly to the second embodiment,the search unit 81 can easily specify, for example, eight beams 46 a to46 h around the specific beam 45 concerned by using a generated dosedistribution table.

The setting unit 82 sets a plurality of combinations each composed ofpre-set J beams out of searched m proximity beams. In the example ofFIG. 21, since the eight proximity beams 46 a to 46 h around thespecific beam 45 concerned have already been searched, a plurality ofcombinations each composed of, for example, five proximity beams arerandomly set out of the eight proximity beams 46 a to 46 h. It ispreferable to acquire a plurality of combinations by selecting Jproximity beams from the m proximity beams by a round robin method.

Next, the writing control unit 72 calculates, for each specified beam, adifference dose D′ for redistribution by subtracting a threshold Dthfrom an incident dose D of the control grid 27 corresponding to thespecific beam 45 concerned. The incident dose D of the control grid 27corresponding to the specific beam 45 concerned, and the incident dose Dof each of the eight control grids 27 corresponding to, for example,peripheral eight proximity beams 46 a to 46 h can be referred to fromthe dose map (2).

Next, for each combination, until the difference dose D′ becomes zero,the redistribution unit 83 assigns a portion of the difference dose D′,as a redistribution dose, from smallest to largest in the order ofincident dose D of J control grids 27 corresponding to J proximity beamsof the combination concerned until reaching respective thresholds Dth.Alternatively, it is also preferable that the redistribution unit 83uniformly assigns, for each combination, a dose equivalent toredistribution dose D′/J, obtained by dividing the difference dose D′ byJ being the number of beams, to each of the control grids 27corresponding to the J proximity beams of the combination concerned.Here, since J being the number of beams configuring a combination can beset arbitrarily, generation of redistribution remnants of the differencedose D′ can be substantially avoided.

The gravity center calculation unit 84 calculates, for each combination,the position of the gravity center of a dose to be redistributed to eachproximity beam.

Next, the selection unit 85 (redistribution beam selection unit)selects, as a plurality of proximity beams serving as redistributiondestinations, a proximity beam combination with respect to whichdeviation of the position of the gravity center due to redistribution isleast, from a plurality of combinations. Specifically, it operates asdescribed below. The selection unit 85 selects, as a J (plural)proximity beams serving as redistribution destinations, a proximity beamcombination (composed of J beams) with respect to which the position ofthe gravity center of each redistribution dose to be redistributeddeviates least from the irradiation position (e.g., irradiation position39 c) of the specific beam 45 concerned.

The modulating unit 86 performs dose modulation, for each proximity beamof the selected proximity beam combination (composed of J beams), byadding each distribution dose to the incident dose D of the control grid27 corresponding to the proximity beam concerned. Similarly, theincident dose D of the control grid 27 corresponding to the specificbeam whose incident dose D exceeds the threshold Dth is modulated to bethe threshold Dth.

By the process described above, it is possible to eliminate the controlgrid 27 whose incident dose D exceeds the threshold Dth. The contents ofthe writing step (S140) are the same as those of the first embodiment.

FIGS. 25A and 25B show examples of dispersion at the edge due to dosedistribution and a dose frequency according to the third embodiment.FIG. 25A shows a comparative example in the case where dispersion at theedge can be reduced to 1.08 nm (3σ) and the maximum dose can be reducedto 1.67 by the configuration for performing distribution to four pointsaccording to the first embodiment. This comparative example shows thecase of writing a pattern different from that of the example shown inFIGS. 16A and 16B. In that case, although the value of dispersion of 3σat the edge deteriorates to 1.91 nm due to dose modulation performed inthe third embodiment as shown in FIG. 25B, it turns out that the maximumdose has been decreased to 1.21.

According to the third embodiment, since redistribution is performedwhile shifting the position of the center of gravity for a portion ofthe dose which has originally been distributed with consideration fornot changing the position of the center of gravity, positional deviationcan be as small as possible even though it occurs a little.

According to the third embodiment, the adjustment width of dosemodulation can be reduced much more than that of the first embodiment,thereby further improving the throughput.

Embodiments have been explained referring to specific examples describedabove. However, the present invention is not limited to these specificexamples. For example, although, in the above-described example,deviation of the position of the gravity center is calculated whenselecting a combination to be redistributed, it is not limited thereto.It is also preferable to select a combination with respect to which thesum total of a value obtained by multiplying a squared distance from thetarget reference position (e.g., position of control grid) by a doseafter redistribution is smallest.

While the case of inputting a 10-bit control signal into each controlcircuit 41 has been described above, the number of bits may be suitablyset. For example, a 2-bit (or 3 to 9 bit) control signal may be used.Alternatively, a control signal of 11-bits or more may be used.

While the apparatus configuration, control method, and the like notdirectly necessary for explaining the present invention are notdescribed, some or all of them can be selectively used case-by-casebasis. For example, although description of the configuration of thecontrol circuit for controlling the writing apparatus 100 is omitted, itshould be understood that some or all of the configuration of thecontrol circuit can be selected and used appropriately when necessary.

In addition, any other multiple charged particle beam writing apparatusand multiple charged particle beam writing method that include elementsof the present invention and that can be appropriately modified by thoseskilled in the art are included within the scope of the presentinvention.

Additional advantages and modification will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A multiple charged particle beam writingapparatus comprising: an emission source configured to emit a chargedparticle beam; a shaping aperture array substrate configured to formmultiple charged particle beams by being irradiated with the chargedparticle beam; a combination setting circuitry configured to set, foreach of a plurality of design grids being irradiation positions indesign of the multiple charged particle beams, a plurality ofcombinations each composed of three beams whose actual irradiationpositions surround a design grid concerned in the plurality of designgrids, by using four or more beams whose actual irradiation positionsare close to the design grid concerned; a first distribution coefficientcalculation circuitry configured to calculate, for each of the pluralityof combinations, a first distribution coefficient for each of the threebeams configuring a combination concerned in the plurality ofcombinations, for distributing a dose to irradiate the design gridconcerned to the three beams configuring the combination concerned suchthat a position of a gravity center of each distributed dose coincideswith a position of the design grid concerned and a sum of the eachdistributed dose coincides with the dose to irradiate the design gridconcerned, where at least one the first distribution coefficient iscalculated for the each of the four or more beams; a second distributioncoefficient calculation circuitry configured to calculate, for each ofthe four or more beams, a second distribution coefficient of the each ofthe four or more beams relating to the design grid concerned by dividinga total value of the at least one the first distribution coefficientcorresponding to a beam concerned in the four or more beams by a numberof the plurality of combinations; and a writing mechanism configured towrite a pattern on a target object with the multiple charged particlebeams in which the dose to irradiate each of the plurality of designgrids has been distributed to each corresponding one of the four or morebeams.
 2. The apparatus according to claim 1, wherein the dose toirradiate the each of the plurality of design grids is distributed tofour beams whose actual irradiation positions are close to the designgrid concerned, further comprising: a proximity beam selection circuitryconfigured to select, for the each of the plurality of design grids, asthe four beams whose actual irradiation positions are close to thedesign grid concerned, a beam corresponding to a closest irradiationposition in each of four regions obtained by being divided by twostraight lines which pass the design grid concerned and have differentangles.
 3. The apparatus according to claim 1, further comprising: aredistribution circuitry configured to redistribute, with respect to abeam whose received distributed dose exceeds a threshold if the dose toirradiate the design grid concerned has been distributed, a portion of adistribution dose to be distributed to the beam, to a plurality of beamsaround the beam concerned.
 4. The apparatus according to claim 3,further comprising: a redistribution beam selection circuitry configuredto select, as the plurality of beams serving as redistributiondestinations, a beam combination, with respect to which deviation of aposition of a gravity center due to redistribution is least, from aplurality of combinations.
 5. The apparatus according to claim 1,further comprising: a dose map generation processing circuitryconfigured to generate a dose map which defines an incident dose for theeach of the plurality of design grids.
 6. The apparatus according toclaim 1, further comprising: a beam-positional-deviation map generationcircuitry configured to generate a firstbeam-positional-deviation-amount map which defines a positionaldeviation amount of each beam of the multiple charged particle beams. 7.The apparatus according to claim 6, wherein thebeam-positional-deviation map generation circuitry further generates asecond beam-positional-deviation-amount map for the each of theplurality of design grids, using the firstbeam-positional-deviation-amount map.
 8. The apparatus according toclaim 7, wherein the actual irradiation positions are obtained using thesecond beam-positional-deviation-amount map.
 9. The apparatus accordingto claim 1, further comprising: a dose distribution table generationcircuitry configured to generate a dose distribution table in which thesecond distribution coefficient for the each of the four or more beamsis defined relating to a target design grid of the plurality of designgrids.
 10. A multiple charged particle beam writing method comprising:setting, for each of a plurality of design grids being irradiationpositions in design of multiple charged particle beams, a plurality ofcombinations each composed of three beams whose actual irradiationpositions surround a design grid concerned in the plurality of designgrids, by using four or more beams whose actual irradiation positionsare close to the design grid concerned; calculating, for each of theplurality of combinations, a first distribution coefficient for each ofthe three beams configuring a combination concerned in the plurality ofcombinations, for distributing a dose to irradiate the design gridconcerned to the three beams configuring the combination concerned suchthat a position of a gravity center of each distributed dose coincideswith a position of the design grid concerned and a sum of the eachdistributed dose coincides with the dose to irradiate the design gridconcerned, where at least one the first distribution coefficient iscalculated for the each of the four or more beams; calculating, for eachof the four or more beams, a second distribution coefficient of the eachof the four or more beams relating to the design grid concerned bydividing a total value of the at least one the first distributioncoefficient corresponding to a beam concerned in the four or more beamsby a number of the plurality of combinations; and writing a pattern on atarget object with the multiple charged particle beams in which the doseto irradiate each of the plurality of design grids has been distributedto each corresponding one of the four or more beams.